Thermosensitive and crosslinkable polymer composite for three-dimensional soft tissue scaffold printing

ABSTRACT

A hydrogel material for use in three-dimensional scaffold printing is disclosed. The material is formed from a first triblock polymer having a formula ABA and a second triblock polymer having a formula AmaBAma, wherein A is a first polymer, B is a second polymer, and Ama is a methacrylate of the first polymer. The material is thermosensitive and photocrosslinkable. A method of manufacturing the material is also disclosed.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims the benefit of the filing date of U.S.provisional application No. 61/676,466, filed on Jul. 27, 2012, theteachings of which are incorporated herein by reference.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

This invention was made with government support under Contract No.CMMI-0700139 awarded by the National Science Foundation. The governmenthas certain rights in the invention.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a thermosensitive andphotocrosslinkable composite material that may be used inthree-dimensional scaffold printing.

2. Description of the Related Art

In the US alone, around eight million surgical procedures are performedevery year to treat maladies related to damaged tissue; over 70,000patients are waiting for organ transplants, and more than 100,000 peopledie each year with tissue related disorders. The current demands forreplacement organs and tissues far exceed the supply, and researchindicates that this gap will continue to widen. The history ofreconstructive surgery began with ablative surgery, followed by tissueand organ transplantation, leading to contemporary tissuereconstruction. In recent years, the main focus of tissue engineeringhas been on the culture of cells. In general, tissues arethree-dimensional (“3-D”) structures composed of living cells and asupport structure. Therefore, the generation of functional implants fromliving cells relies heavily on the fabrication of the 3-D structure.Tissue engineering has been successfully used to replace skin, bloodvessels, and cardiac tissue. For a new generation of complex 3-Dimplants, more sophisticated technology is required. Complex shapes andstructures can be created from special biodegradable and biocompatiblepolymers so that a tissue's natural support structure replaces thesynthetic scaffold as it degrades. The materials should therefore beconsidered only as a temporary support for cell growth and celladhesion. For engineering soft tissues, ideal scaffolds are made ofsynthetic or natural biopolymers providing porous (up to 90%) supportstructure, thus mimicking the natural extracellular matrix environmentin which cells attach, multiply, migrate and function. The pores in thescaffold must be interconnected to allow efficient nutrient transfer andwaste exchange to permit survival of any cells cultured on the scaffold.The pores should typically be 100-300 μm, around 5-10 times a cell'sdiameter. Porous scaffolds facilitate tissue formation while providingadequate mechanical strength to withstand implantation and permit normalphysiological function in the human body.

There exists a need for a temporary scaffolding material that isthermoresponsive and photocrosslinkable as well as designed andfabricated to be used in many different applications of solid freeformfabrication.

SUMMARY OF THE INVENTION

This Summary is provided to introduce a selection of concepts in asimplified form that are further described below in the DetailedDescription. This Summary is not intended to identify key features oressential features of the claimed subject matter, nor is it intended tobe used to limit the scope of the claimed subject matter.

In one embodiment, the present invention is a hydrogel material for usein three-dimensional scaffold printing is disclosed. The material isformed from a first triblock polymer having a formula ABA and a secondtriblock polymer having a formula AmaBAma, wherein A is a first polymer,B is a second polymer, and Ama is a methacrylate of the first polymer.The material is thermosensitive and photocrosslinkable.

In another embodiment, the present invention is a method of forming ahydrogel material comprising the steps of: providing a first triblockpolymer having a formula ABA; blending a second triblock polymer havinga formula AmaBAma with the first triblock polymer, forming a blend,wherein A is a first polymer, B is a second polymer, and Ama is amethacrylate of the first polymer; and heating the blend to betweenabout 33 degrees Celsius and about 34 degrees Celsius.

BRIEF DESCRIPTION OF THE DRAWINGS

Other aspects, features, and advantages of the present invention willbecome more fully apparent from the following detailed description, theappended claims, and the accompanying drawings in which like referencenumerals identify similar or identical elements.

FIG. 1 shows the chemical formation of a PEG-PLGA diblock polymer;

FIG. 2 shows the chemical formula of a PEG-PLGA-PEG triblock polymer;

FIG. 3 shows the formation of a PEG-PLGA-PEG micelle;

FIG. 4 shows the concentration of the PEG-PLGA-PEG micelle in water;

FIG. 5 shows the chemical formula of a PEGma-PLGA-PEGma triblockpolymer;

FIG. 6 shows a table of viscosities, temperatures, and elastic modulifor various mix ratios of PEG-PLGA-PEG/PEGma-PLGA-PEGma;

FIG. 7 shows a graph of Viscosity v. Temperature for a 20/80 blend ofPEG-PLGA-PEG/PEGma-PLGA-PEGma;

FIG. 8 shows a graph of elastic storage shear modulus and loss, orviscous, shear modulus v. Temperature for a 20/80 blend ofPEG-PLGA-PEG/PEGma-PLGA-PEGma; and

FIG. 9A shows a side elevation view of a plurality of drops of thePEG-PLGA-PEG/PEGma-PLGA-PEGma blend prior to ultraviolet irradiation;

FIG. 9B shows a top plan view of the plurality of drops shown in FIG.9A;

FIG. 9C shows a top plan view of the plurality of drops afterultraviolet irradiation; and

FIG. 9D shows a side elevation view of the plurality of drops shown inFIG. 9C.

DETAILED DESCRIPTION

In the drawings, like numerals indicate like elements throughout.Certain terminology is used herein for convenience only and is not to betaken as a limitation on the present invention. The terminology includesthe words specifically mentioned, derivatives thereof and words ofsimilar import. The embodiments illustrated below are not intended to beexhaustive or to limit the invention to the precise form disclosed.These embodiments are chosen and described to best explain the principleof the invention and its application and practical use and to enableothers skilled in the art to best utilize the invention.

Reference herein to “one embodiment” or “an embodiment” means that aparticular feature, structure, or characteristic described in connectionwith the embodiment can be included in at least one embodiment of theinvention. The appearances of the phrase “in one embodiment” in variousplaces in the specification are not necessarily all referring to thesame embodiment, nor are separate or alternative embodiments necessarilymutually exclusive of other embodiments. The same applies to the term“implementation.”

As used in this application, the word “exemplary” is used herein to meanserving as an example, instance, or illustration. Any aspect or designdescribed herein as “exemplary” is not necessarily to be construed aspreferred or advantageous over other aspects or designs. Rather, use ofthe word exemplary is intended to present concepts in a concretefashion.

Additionally, the term “or” is intended to mean an inclusive “or” ratherthan an exclusive “or”. That is, unless specified otherwise, or clearfrom context, “X employs A or B” is intended to mean any of the naturalinclusive permutations. That is, if X employs A; X employs B; or Xemploys both A and B, then “X employs A or B” is satisfied under any ofthe foregoing instances. In addition, the articles “a” and “an” as usedin this application and the appended claims should generally beconstrued to mean “one or more” unless specified otherwise or clear fromcontext to be directed to a singular form.

Unless explicitly stated otherwise, each numerical value and rangeshould be interpreted as being approximate as if the word “about” or“approximately” preceded the value of the value or range.

The use of figure numbers and/or figure reference labels in the claimsis intended to identify one or more possible embodiments of the claimedsubject matter in order to facilitate the interpretation of the claims.Such use is not to be construed as necessarily limiting the scope ofthose claims to the embodiments shown in the corresponding figures.

It should be understood that the steps of the exemplary methods setforth herein are not necessarily required to be performed in the orderdescribed, and the order of the steps of such methods should beunderstood to be merely exemplary. Likewise, additional steps may beincluded in such methods, and certain steps may be omitted or combined,in methods consistent with various embodiments of the present invention.

Although the elements in the following method claims, if any, arerecited in a particular sequence with corresponding labeling, unless theclaim recitations otherwise imply a particular sequence for implementingsome or all of those elements, those elements are not necessarilyintended to be limited to being implemented in that particular sequence.

Hydrogels have been widely used in various biomedical applications,including tissue engineering, due to their biocompatibility, lowtoxicity and low cost. Hydrogels are hydrophilic polymer networks thatcan absorb up to a thousand times their dry weight in water. Their highwater contents make them more similar to native tissues than dry porouspolymer scaffolds. Hydrogels can either be chemically stable ordegradable which eventually disintegrate and dissolve. Hydrogels arecalled ‘physical’ gels when the networks are held together by molecularentanglements and/or secondary forces including ionic, hydrogen-bondingor hydrophobic forces. Physical hydrogels are not homogeneous, sinceclusters of molecular entanglements, or hydrophobically- orionically-associated domains, can create inhomogeneities. Free chainends or chain loops also represent transient network defects in physicalgels. The polymer chains can be easily modified to vary the resultanthydrogel properties to fit the application. For tissue engineering(“TE”) purposes, hydrogels may be functionalized to promote cellproliferation, migration and adhesion. In addition, hydrogels are highlypermeable, which facilitates exchange of oxygen, nutrients, and otherwater soluble metabolites, making them ideal for cell encapsulation. Thehydrophilicity inhibits protein adsorption, thereby minimizing theforeign body responses when implanted in vivo.

A novel material has been developed that is capable of being used innumerous types of solid freeform fabrication (“SFF”) printers to print3-dimensional scaffolds for soft tissue. A 20/80 mix of low molecularweight poly(ethylene glycol-b-(DL-lactic acid-co-glycolicacid)-b-ethylene glycol) PEG-PLGA-PEG and low molecular weightPEGma-PLGA-PEGma triblock copolymer dissolved with Irgacure® 2959(manufactured by CIBA®) in de-ionized (“DI”) water produced a materialthat is of low viscosity to allow for easy movement through SFFprinters. This biocompatible and degradable material possesses a twostage gelation process. It is a non-viscous 228 centipoise (“cP”)solution at 20° C. and quickly transitions to a more 122,836 cP viscousmaterial with an increase in temperature to 33° C. To increase thematerial properties further and create a network of irreversiblecrosslinks, irradiation of UV light is used. This material accomplishesall necessary requirements for it to be applicable for SFF printers: 1)low viscous solution before printing, 2) no mixing is needed to form ahomogenous gel, 3) has a short solution to gel transition time, 4)mechanically strong material to allow for vertical building, and 5)irreversible gel to prevent deformation of the final printed structure.

A photocrosslinkable material permits quick gelation and eliminated theneed for multiple print heads since it does not need anothercrosslinking material. The challenges with photocrosslinkable materialwas the UV light irradiation source and the ability of a droplet ofmaterial to hold its shape after printing before gelation.Thermosensitive materials were able to gel rapidly allowing for materialto hold its shape after printing but, unlike photocrosslinkablematerial, was reversible. To be able to create a thermosensitivematerial with the mechanical properties to allow for 3-dimensionalbuilding, a high viscous initial material was needed after printing andbefore irradiation. The combination of thermosensitive andphotocrosslinkable material met every need for SFF printing.

A thermosensitive material, PEG-PLGA-PEG, was examined as well as themechanism of gelation and the effect of altering the molecular weightsof the PEG and PLGA. PEG-PLGA-PEG, dissolved in water, becomes a gel astemperature increases past its sol-to-gel transition point because ofthe formation of micelles in the material. PLGA is hydrophobic and isthe driving force of micelle formation. As temperature increases, thePLGA parts of the copolymer chains clump together with the PEG compoundsinteracting with the water because of its hydrophilicity. The micellescontinue to grow as temperature increases. The formation of micelles isshown in FIG. 3. The concentration of PEG-PLGA-PEG determines thestiffness of the resulting structure, as exemplified in FIG. 4.

To help increase the mechanical properties and long term stability ofthe gel, Irgacure 2959, a photoinitiator, was added to the triblock.Irgacure 2959 works by breaking double bonds between carbon molecules,stabilizing that bond, and then repeating. Irgacure 2959 breaks apartinto free radicals once it is initiated by UV light irradiation. Thefree radicals are what break apart the carbon double bonds because theyare less stable than single carbon bonds. The radicals start a chainreaction of breaking apart carbon double bonds and securing otheravailable free carbons to form a network of crosslinks. PEG-PLGA-PEGdoes not have any available carbon double bonds for Irgacure to break soa different type of PEG was needed since the PEG was the outsidecomponent of the triblock with an available free end. PEG methacrylatewas substituted for the original PEG methyl ether.

A material that was a combination of PEG-PLGA-PEG and PEGma-PLGA-PEGmawith Irgacure 2959 gelled thermally and possessed the ability tocrosslink with UV light. Four different types of mixes ofPEG-PLGA-PEG/PEGma-PLGA-PEGma were prepared and compared: 50/50, 35/65,20/80, and 10/90. A final polymer concentration of 45% in water was usedsince this percentage consistently had the best material properties asshown in previous tests. As the ratio increased from 50/50 to 20/80, thematerial became more viscous thermally and stiffer as a UV crosslinkedmaterial. Above 20/80, the 10/90 material's properties declined andlooked similar to the properties of PEGma-PLGA-PEGma material. The 20/80mix was found to have the highest maximum viscosity of 122,836 cP, whichis comparable to sour cream and peanut butter, and also have the highestelastic modulus. The elastic modulus was reached at the lowesttemperature, helping to prevent evaporation of the water content. Aftermicelle formation, the 50/50, 35/65, and 20/80 mixes of materials areable to hold its shape allowing for UV irradiation to create permanentcrosslink and increase the mechanical properties of the material. The20/80 mix had the highest solution viscosity, 228 cP, but the value isstill within the range of viscosity that most SFF printers are capableof handling. The 20/80 mix also had the highest elastic modulus as agel, 93.9 Pascals (Pa), of all materials tested. Thermally, the materialdid not technically form a gel since the elastic modulus was nevergreater than the viscous modulus but the material was stiff enough to beable to hold its shape before UV irradiation. This material retained thebest photosensitivity of all mixed triblock polymer materials; it gelledthe quickest and was able to hold its shape and even hold a shape it wasmolded into.

A 20/80 mix of low molecular weight PEG-PLGA-PEG and low molecularweight PEGma-PLGA-PEGma mixed with Irgacure 2959 gelled with the help oftemperature and UV irradiation and is capable of 3-D building. Thismaterial mixed with de-ionized water forms a material that has lowviscosity as a solution at low temperature and is capable of drasticallyincreasing viscosity and mechanical properties at a temperature of about33° C. This material is capable of holding its 3-D shape in order for UVirradiation to further increase the mechanical properties and form anirreversible network of crosslinks to confirm that the structure of thematerial will be permanent before degradation of the materials occur.

In an exemplary embodiment, a hydrogel material according to the presentinvention is composed of a blend of a first triblock polymer having aformula ABA and a second triblock polymer having a formula AmaBAma. A isa first polymer, B is a second polymer, and Ama is a methacrylate (“ma”)of the first polymer. In a further exemplary embodiment, A ishydrophilic material, such as polyethylene glycol (PEG), and B is ahydrophobic material, such as poly(DL-lactic acid-co-glycolic acid)(PLGA), such that ABA has a specific formula PEG-PLGA-PEG and AmaBAmahas a specific formula PEGma-PLGA-PEGma.

The exemplary blend comprises about 20 percent by weight of PEG-PLGA-PEGand about 80 percent by weight of PEGma-PLGA-PEGma. The PEG has amolecular weight of about 550 and the PLGA has a molecular weight ofabout 2810, such that the PLGA has a molecular weight about 5.1 timesthe molecular weight of the PEG. Additionally, the PEGma has a molecularweight of about 526 such that the PLGA has a molecular weight about 5.3times the molecular weight of the PEGma.

To synthesis the PEG-PLGA-PEG polymer, polyethylene glycol (PEG) methylether (Mn=550, 750, and 1,000 g/mol), DL-lactide (DLLA), glycolide (GA),anhydrous toluene, and hexamethylene diisocynate (HMDI) were all used.All solvents and other chemicals are of analytical grade.

PEG is typically terminated with hydroxyl groups which can serve as apoint of synthetic modification. The free hydroxyl groups of PEG arering-opening initiators for lactide and glycolide. Lactide and glycolidein the molar ratio of 78/22 were used to create a PLGA material ofmolecular number 1405. Ring opening polymerization of lactide andglycolide onto monomethoxypoly(ethylene glycol), molecular weight of550, using stannous octoate (tin(II) 2-ethylhexanoate) (SnOct) as thecatalyst was performed to synthesize PEG-PLGA diblock copolymers, shownin FIG. 1.

In ring opening polymerization, the terminal end of the polymer, thehydroxyl end group (—OH) of the PEG, acts as a reactor and breaks aparta cyclic monomer, Glycolide and DLLA, to form a large polymer chain. Thepolymer chain that is formed is the diblock polymer PEG-PLGA. Anhydroustoluene was added as a solvent in the reaction. The materials were mixedin a covered, but not sealed, ball flask at 130° C. in an oil bath for24 hours. Ester bonds form in the reaction between PLGA and PEG whilethe byproduct of H2O was evaporated off during the reaction. Thecopolymer was then coupled by adding HMDI and was mixed in an oil bathat 60° C. for 12 hours. The final product was two PEG-PLGA diblockscoupled in the middle with HMDI to form a PEG-PLGA-HMDI-PLGA-PEG polymerchain. The chemical structure of the resulting polymer chain is shown inFIG. 2.

Because the HMDI coupler of the two PLGA chains is somewhatinsignificant compared to the high molecular weight PLGA and PEG, theproduct is considered a triblock copolymer, PEG-PLGA-PEG, with a largePLGA chain between two PEG components. HMDI was added in a 0.5 molarequivalence to the mass of the PEG. A reflux was then performed at 110°C., the boiling temperature of toluene, for 12 hours. Afterward, thematerial was precipitated in cold diethyl ether, dissolved indichloromethane (DCM), and then re-precipitated in cold diethyl ether toremove any impurities. Finally, the PEG-PLGA-PEG triblock copolymer wasplaced in a vacuum oven overnight to remove any residual solvents. Thematerial was then stored at −20° C. to prevent any degradation of thePLGA.

Additional steps involving rotoevaporation were added later to helpguarantee the absence of unwanted solvents, including toluene, diethylether, and dichloromethane. Rotoevaporating, or rotary evaporator,entails using a device to efficiently and gently remove solvents fromsamples by evaporation. The sample is places in a ball flask and rotatedwhile in a hot bath of water or oil. The contents are put under vacuumto help assist in quickly evaporating any excess solvents. The rotarymotion allows for more surface area for solvents to evaporate quicker.These two additional rotoevaporation steps were added after the refluxand after the copolymer was re-precipitated in dichloromethane. Therotoevaporation was conducted at 80° C. and under vacuum.

The synthesis of PEGma-PLGA-PEGma is almost identical to the synthesisof PEG-PLGA-PEG. Using PEG methacrylate (Mw=526), ring openingpolymerization to form diblocks and coupling of the diblocks to formtriblocks proceeded. The material was rotoevaporated under vacuum for 30minutes in a water bath at 85° C. before being dissolved indichloromethane and then precipitated in cold diethyl ether to removeany impurities. Again, the material was rotoevaporated and then wasplaced in a vacuum oven overnight to remove any residual solvents andfinally stored at −20° C. to prevent degradation of the PLGA. Theresulting PEGma-PLGA-PEGma has the formula shown in FIG. 5.

To prepare the triblock copolymer for printing, DI water was added andthe solution was stirred at 4° C. for 24 hours with constant inspectionto ensure homogeneity. The product was then characterized byspectroscopy and rheology to determine its molecular composition,viscosity, and elastic and viscous moduli.

At a maximum viscosity of 122,836 cP, similar to sour cream and peanutbutter, a 20/80 mix of PEG-PLGA-PEG and PEGma-PLGA-PEGma had thegreatest viscosity of mix ratios of 50/50, 35/65, 20/80, and 10/90, asshown in FIG. 6. It also had the highest solution minimum viscosity of228 cP, which is shown in FIG. 7. The 20/80 mix of material observed theclosest maximum viscosity and maximum elastic modulus temperatures of33.3° C. and 33.98° C. respectively. The material did not technicallygel when the elastic modulus was at its maximum but as the temperatureincreased, elastic storage shear modulus did become greater than loss,or viscous, shear modulus, as shown in FIG. 8. High elastic and viscousmoduli data and the increase in viscosity at extreme high temperatureare due to some water evaporation during testing. This material was ableto fully and irreversibly gel under UV light in less than 1 minute. Itis possible to view a 3-D structure with the 20/80 gel due to the quickphotoresponsiveness of the material.

To further test the 3-D building ability of the 20/80 material, a row ofdroplets were pipetted onto a glass slide, as shown in FIGS. 9A and 9B.A series of droplets on top of the old droplets were repeated aftergelation of the previous droplet. After 10 seconds of UV lightirradiation for each round of droplets, another round of droplets wasplaced. As shown in the final gelation pictures of FIGS. 9C and 9D, thematerial is capable of holding its shape and building vertically. Toalso demonstrate the shape holding aspects of this material, some of thedroplets were peeled back off of the glass slide (not shown).

An exemplary method of manufacturing the inventive material includes thesteps of providing the first triblock polymer having the formula ABA,such as, for example, PEG-PGLA-PEG and blending the second triblockpolymer having the formula AmaBAma, such as, for example,PEGma-PLGA-PEGma, with the first triblock polymer, forming a blend. Theratio of PEG-PLGA-PEG to PEGma-PLGA-PEGma is about 20/80 by weight. Thetwo polymers are mixed in DI water to form a solution with about 0.03percent by weight of a photoinitiator.

The blend can be used in a SFF printer for 3-D printing of scaffoldmaterial. The blend is heated as it is ejected from the printer tobetween about 33 degrees Celsius and about 34 degrees Celsius, raisingthe viscosity of the blend from less than about 230 cP to over about122,000 cP and raising the maximum elastic modulus to over about 93Pascals. The blended material is then irreversibly crosslinked byirradiating the blend with ultraviolet light. In an exemplaryembodiment, the blend is irradiated with a 365 nanometer ultravioletlight after about 10 layers of the material are deposited onto asubstrate (not shown).

Degradation is important in tissue engineering materials to allow forencapsulated cells and growth of surrounding tissue into the scaffold.Another advantage of degradation is to allow for drug delivery at therepaired site. The drug release of spironolactone in PBS was studiedfrom a PEG-PLGA-PEG (550-2810-550) triblock material and was found tofully release after 58 days. The benefit of using a PEG-PLGA-PEGmaterial is that the PLGA is biodegradeable, which permits the releaseof drugs and the growth of cells. The degradation rate of PLGA has beenresearched and found to depend on several factors includingD,L-lactide-glycolide (“DLLA:GA”) ratio, molecular weight, and watercontent.

Because the degradation rate of the PLGA is adjustable, based on thesefactors, the degradation rate of the inventive material can also beadjusted accordingly. Further, adjusting the ratio ofPEG-PLGA-PEG/PEGma-PLGA-PEGma from 20/80 to other values also adjuststhe degradation rate of the material.

It is desired that the inventive material degrade over time so that itcan be replaced by live tissue growing through the scaffold.

The inventive material has an elastic modulus that is compatible withhuman soft tissue, such as, for example, the heart and liver, and cantherefore be used as scaffold material in conjunction with such organs.

It will be further understood that various changes in the details,materials, and arrangements of the parts which have been described andillustrated in order to explain the nature of this invention may be madeby those skilled in the art without departing from the scope of theinvention as expressed in the following claims.

We claim:
 1. A hydrogel material comprising: a first triblock polymerhaving a formula ABA; and a second triblock polymer having a formulaAmaBAma, wherein: A is polyethylene glycol; B is poly(DL-lacticacid-co-glycolic acid); and Ama is a methacrylate of the first polymer,wherein the material is thermosensitive and photocrosslinkable.
 2. Thehydrogel material according to claim 1, wherein about 20 percent byweight of the blend comprises the first triblock polymer and about 80percent by weight of the blend comprises the second triblock polymer. 3.A hydrogel material comprising: a first triblock polymer having aformula ABA; and a second triblock polymer having a formula AmaBAma,wherein: A is a first polymer; B is a second polymer; and Ama is amethacrylate of the first polymer, wherein the material isthermosensitive and photocrosslinkable and wherein A has a firstmolecular weight, and wherein B has a second molecular weight, about 5.1times the first molecular weight.
 4. The hydrogel material according toclaim 1, wherein about 0.03 percent by weight of the blend comprises aphotoinitiator.
 5. The hydrogel material according to claim 1, whereinthe material has a maximum viscosity of over about 122,000 centipoise ata temperature between about 33 degrees Celsius and about 34 degreesCelsius.
 6. The hydrogel material according to claim 1, wherein thematerial has a maximum elastic modulus of over about 93 Pascals at atemperature between about 33 degrees Celsius and about 34 degreesCelsius.
 7. The hydrogel material according to claim 1, wherein A is ahydrophilic material and wherein B is a hydrophobic material.
 8. Amethod of manufacturing a polymer composite comprising the steps of: (a)providing a first triblock polymer having a formula ABA; (b) blending asecond triblock polymer having a formula AmaBAma with the first triblockpolymer, forming a blend, wherein: A is polyethylene glycol; B ispoly(DL-lactic acid-co-glycolic acid); and Ama is a methacrylate of thefirst polymer; and (c) heating the blend to between about 33 degreesCelsius and about 34 degrees Celsius.
 9. The method according to claim8, further comprising providing about 0.03 percent by weight of aphotoinitiator.
 10. The method according to claim 8, wherein step (c)comprises raising the viscosity of the blend to over about 122,000centipoise.
 11. The method according to claim 8, wherein step (c)comprises raising the maximum elastic modulus to over about 93 Pascals.12. The method according to claim 8, wherein, prior to step (c), theblend has a viscosity of less than about 230 centipoise.
 13. The methodaccording to claim 8, further comprising, after step (c), irradiatingthe blend with ultraviolet light.
 14. The method according to claim 8,further comprising providing about 20 percent by weight of the firsttriblock polymer and about 80 percent by weight of the second triblockpolymer for the blend.
 15. The method according to claim 8, furthercomprising, prior to step (c), dissolving the blend in water.